I was trying to change the interface graphics and everything was going fine, but when I tried to change the fonts (SMALLFNT and BIGFONT) it seems to not work.
The HUD and it's elements are working. A part of the code to show how I'm doing it (I have the graphics in the same PK3 so it works):

Single lump fonts are not a graphic so you can't scale them like that. To do high resolution fonts you need to split the characters into individual graphics and then scale those. Use FONTDEFS to build a font out of the graphics.